Solar panels produce the most when sunlight hits them square on. The sun sits lower in winter and higher in summer, and the further you are from the equator the lower it sits overall. That is why the best angle depends mainly on your latitude.
How the angle is calculated
For a fixed panel, the year-round angle uses a widely quoted fit to simulated yearly output: about 0.87 × latitude within 25° of the equator, and 0.76 × latitude + 3.1° further out. The seasonal angles are 15° steeper for winter and 15° flatter for summer.
The calculator never goes below 10°. An almost-flat panel stops rinsing clean when it rains, and in dusty places a dirty panel loses more than a perfect angle gains. For why output drops in the cold months even with a good angle, see solar panels producing less in winter.
Measuring tilt on the roof
Tilt is measured from flat ground, so 0° lies flat and 90° stands upright. A free angle-finder app on a phone laid along the panel frame is accurate enough. On pitched roofs panels normally follow the roof, and a roof within 10–15° of the ideal is fine as it is.
Your location
"Use my location" asks your browser for your position and uses only the latitude. It is worked out in the page and never sent anywhere.
Common questions
Is solar panel tilt equal to latitude?
Close, but for fixed panels the best year-round angle is a little flatter than latitude once you are more than about 25° from the equator, because summer days are long and bright. At 40° north, around 33° collects slightly more over a year than 40°.
How much power do I lose with the wrong tilt?
Less than most people fear. Being 10–15° away from the ideal typically costs only a few percent a year. Shade, dust and facing the wrong direction cost far more. A flat roof at 10–15° is usually a fine compromise.
Which direction should solar panels face?
Towards the equator: true south in the northern hemisphere and true north in the southern hemisphere. Use true rather than magnetic direction; a phone compass needs correcting for local declination. East or west facing panels still work, with a noticeable loss.
Should I change the angle of my panels in winter?
Tilting about 15° steeper for winter and 15° flatter for summer gains a few percent a year. It is worth it on ground mounts that are easy to adjust, and rarely worth climbing onto a roof for.
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